In fact, [Mezentius] is a Homeric hero in all essentials. Virgil's great model for his battle scenes was naturally the Iliad. And as he moulded the figure of a great Italian warrior, no doubt he scanned closely the many Achaean chieftains to find a working model for his Mezentius. It could not be Achilles since Turnus was already cast for that role. Besides, Mezentius was not a young, swift-footed hero but the gray-haired father of a full-grown son. After much thought - or was it a sudden flash of inspiration? - he found his man in the Iliad: Ajax of Salamis, son of Telamon.
In the Iliad, Ajax is a fighter second only to Achilles, and the best man of all on the defense. He was a giant of a man, with a great, tower-like shield, whose finest hour came when Achilles withdrew from the fighting and many of the chieftains had been wounded. Almost single handed he kept the retreat from turning into a rout, defended the wall and ships against Hector, and saved the body of Patroclus from the enemy. He was a man of few words; actions, when most needed, were his forte. While other heroes have their guardian gods to aid them in time of crisis, Ajax fights on unattended by special divine help. Such, I feel sure, was the splendid figure after whose likeness Virgil moulded his warrior Mezentius. Let us now see how he does it.
Mezentius was a huge man wielding a great spear, "as huge as Orion when he stalks through mid sea and his shoulders overtop the waves" (10. 762 ff.). He was a bulwark of defense, unyielding when the odds were greatest, like a great rock that juts out into the sea and braves the raving winds and waves:
ille velut rupes, vastum quae prodit in aequor,
obvia ventorum furiis, expostaque ponto,
vim cunctam atque minas perfert caelique marisque,
ipsa immota manens... [10. 693-96].
At bay, surrounded by foes who shower him with their darts, he is like a boar caught in the toils (10. 707 ff.), a boar that snorts savagely and bristles up his shoulders and none has the courage to come near him. When he takes the offensive, he is like a lion maddened by hunger (723 ff.) that springs on a timid roe or antlered stag. And, when finally he is confronted by Aeneas, he stands there awaiting his onset, unafraid (769-71).
Now if we turn to Book 17 of the Iliad, we shall find these same similes (with some variations in expression and setting) applied to Ajax as he defends the corpse of Patroclus against the Trojans. Covering the body with his great shield (132 f.), he stood fast "like a lion over his young, when the lion is leading his whelps along and hunters come upon them." Later, when things are desperate and the Achaeans give ground, Ajax charges the Trojans bestriding the body (281 ff.) "like a savage wild boar, who among the hills easily scatters the dogs and young men when he turns at bay in the valley." Toward the end of the book (746 if.) the two Ajaxes hold off the Trojans "as a wooded headland holds off water ..." It was evidently this great book of the Iliad, where the courage, the obstinacy, and the fighting qualities of Ajax are so magnificent, that was much in Virgil's mind as he portrayed Mezentius displaying his prowess.
The full article actually argues that Virgil has drawn on three different heroes of Greek myth in crafting the character of Mezentius; Ajax the Great (son of Telamon), Ajax the Lesser (son of Oileus) and Nestor (father of Antilochus).